1. Field of the Invention
The present invention relates to a color filter structure and method thereof, and more particularly, to a color filter structure and method thereof applied to a liquid crystal display (LCD).
2. Description of the Prior Art
Since liquid crystal displays (LCDs) have the advantages of portability, low power consumption, and low radiation, LCDs have been widely used in various portable information products, such as notebooks, personal digital assistants (PDA), etc.
A color filter structure and thin film transistor (TFT) elements of a prior art thin film transistor liquid crystal display (TFT LCD) are respectively formed on different substrates. The TFT elements are formed in a bottom substrate by multiple photo-etching processes (PEP), while the color filter structure is formed on a top substrate by photo processes or halftone printing technology. Moreover, the method of forming the prior art LCD includes steps of forming a black matrix between any two adjacent color filters. The purpose of the black matrixes is to improve contrast of the LCD, prevent the TFT elements from generating light leakage current, and shade the oblique leaking light during operation of the LCD.
Since the top substrate and the bottom substrate are composed of different materials with different coefficients of thermal expansion, alignment error could happen due to high temperature during the assembly process. The alignment error would cause light leakage, thus at present the color filter on array (COA) technology is broadly applied to form the color filter structure over the TFT elements for avoiding the alignment error of the black matrix layer and the data line. In addition, the alignment issue of the color filter structure becomes more and more important while the substrate size enlarges and the LCD resolution increases.
Refer to FIG. 1 to FIG. 3, which are schematic diagrams of forming a prior art color filter structure 22. As shown in FIG. 1, first a black photoresist layer (not shown in FIG. 1) is formed on a glass substrate 10, and a photo process is performed to form a black matrix layer 12. Generally speaking, the black matrix layer 12 contains materials with high shading, low reflectivity, and good adhesion ability, such as chromium or black resin. Then a red color filter layer 14 is formed on the glass substrate 10, and a photo process is performed to form a red color filter array (CFA) 16. The red color filter layer 14 is a positive type photoresist or a photosensitive resin containing 10 to 50 wt % of red dye.
In order to improve filtering effect and enhance reliability of the color filter array, the red color filter array 16 is then irradiated by ultraviolet beams, and heated with an inert gas, such as nitrogen,for avoiding oxidation. The wave-length of the ultraviolet beams is approximately 320 nm, and the energy of the ultraviolet beams is approximately 20J/cm2. The initial temperature range of heating is between 60 and 140° C., and the heating temperature raises at the rate of 1.5° C./sec until the temperature reaches the range between 160 and 220° C. Afterwards, the abovementioned steps are repeated to form a green color filter array 18 and a blue color filter array 20.
However, light leakage problems could happen because the chromium collapses, chromium remains, or the black matrix layer alignment error while forming the black matrix layer. In this case, the black matrix layer is not capable of shading the TFT elements, so that the light leakage current will occur. Additionally, since high-resolution LCDs are required, the critical dimension (CD) needs reducing, such that the accuracy of alignment becomes more important. Furthermore, the method of forming the prior art color filter structure would cause a side lobe between any two adjacent color filters because of the alignment problem and existence of the black matrix layer. The side lobe would influence the alignment direction of crystal molecules, and further interfere with operation of the LCD.